Hi Steve
Seagrass should never be 'wet' cleaned under any circumstances, you will be taking a massive risk if you do.
As for protection it would hardly be worth it to them, as the footfall would soon break down any protection applied.If you do decide to offer some kind of protection then once again don't use any water based products.
It is recommended that Seagrass is professionaly cleaned every six months,you could offer them this using a dry blend system such as Host and in this enviroment it they may well be advised to carry it out every 3 months.
